Diode pumped lasers involve semiconductor diodes which laser when excited by electrical current. The lasing portions of the semiconductors, typically PN junctions, are positioned near a laser medium, such as a crystal, so that laser energy from the semiconductor diodes is directed into the medium, either directly or by lenses. When "pumped" by the laser energy from the diodes, the energy excitation levels build up within the atomic structure of the medium. The medium, which can be elongated round, square or flat can be provided with a mirror or a reflective coating at each or one end, focuses the laser energy along the main axis of the medium. The laser beam exits through one of the mirrors, or through a portion of one of the mirrors that is partially transparent.
The term "laser head" is often used to refer to the assembly which comprises the gain medium, the lasing diode(s), the mirror(s), and any mounting devices which hold those components in their proper positions and alignment. A laser head can also include other components that are directly attached to the laser head assembly, including possibly a housing and any necessary heat sinks. Typically, a laser head will include one or more electrical ports for the leads which supply the electrical energy from an external power source to the laser diode.
The lasing diode used to excite or "pump" a laser medium can be mounted at one end of the medium, or along the side of the medium. Mounting lasers at one end are limited in power since only one diode or a small number of diodes can be mounted in close proximity to the end of the medium mounting. Lasers along the side can be more powerful, since many diodes can be mounted on diode pumped lasers. For additional information on diode pumped lasers see, e.g., W. Koechner, Solid State Laser Engineering (Springer-Verlad, New York, 1988), the article "Diode-Pumped Solid-State Lasers Have Become A Mainstream Technology" by G. T. Forrest in Laser Focus/Electro-Optics, November 1987, pp. 62-74, the article "Advances in Diode Laser Pumps" by W. Streifer et al in IEEE Journal of Quantum Electronics 24 (6): 883-984 (June 1988), and various patents such as U.S. Pat. Nos. 4,864,585; 4,805,177; 4,901,324; and 5,084,886.
In order to obtain optimal laser beam quality and output power it is important to be able to control adjustment of the beam in the axial direction. Typically, most laser diode pumped solid state lasers require complex assemblies and complex alignment equipment to accurately position the optical components. Since these lasers require complex assemblies and alignment equipment, this adds to the cost of the laser. Additionally, these complex assemblies and alignment equipment add to the volume and weight of the laser.
Another problem associated with the use of laser diode pumped solid state lasers is that laser diodes generate substantial amounts of heat and therefore must be cooled if they are to produce substantial outputs. If not properly cooled, high temperatures (i.e., increased vibrations of the atomic lattices in the semiconductor material) can damage or destroy the diodes. The laser medium is also subjected to high heat and must be cooled for comparable reasons. High temperatures can also cause diodes and medium to become misaligned.
The magnitude and importance of the cooling problem can be seen in perspective by considering the efficiencies of diode pumped lasers. Efficiency is measured by dividing the amount of power carried in the laser beam (expressed in watts) by the total wattage consumed by the laser equipment. For a typical side pumped laser to generate a laser beam carrying one watt of energy it must dissipate as much as 100 watts of input energy, most of which must be dissipated as heat. Many lasers which cannot otherwise cope adequately with the problem of cooling must be operated only in a pulsed mode, i.e., their output is limited to short bursts of laser energy. Between pulses, such lasers must be deactivated so that they are allowed to cool. However, it is often desirable to operate lasers in the continuous wave (CW) mode.
Thus, as can be seen, there remains a need for an improved laser diode pumped solid state laser which is simple to assemble and is relatively easy to accurately align the optical components. Also there is a need for improved methods of removing heat from the immediate vicinity of the diode pumped sources and laser gain mediums in diode pumped lasers. There is also a need the other methods of increasing the power and/or efficiency of diode pumped lasers. Any device or arrangement which provides for more efficient use of the excitation energy from the diodes in exciting the laser medium is desirable in every application. Additionally, any configuration which permits a laser head having a limited size to put out a more powerful laser beam is useful in any application where higher power is desirable. Both factors are especially important for lasers that operate in a continuous wave mode and for lasers used in devices where volume and weight are limited or tightly constrained, such as in satellite applications and applications which involve miniaturized electronics.